Spatiotemporal optimization of micro spray mist: effects on growth physiology in apple trees and comprehensive evaluation

Climate change and water scarcity pose serious challenges to apple production in semi-arid northern China. Micro spray mist is a promising irrigation technique that can simultaneously improve soil moisture and modulate canopy microclimate. To clarify the comprehensive response of apple growth and development, photosynthetic index, leaf water status, and canopy temperature and humidity to micro spray mist at different temporal and spatial scales, we conducted a two-factor experiment involving mist duration (T1: 2.0 h, T2: 1.5 h, T3: 1.0 h, T4: 0.5 h) and mist height (H1: upper canopy, H2: middle canopy, H3: lower canopy). Measurements included tree growth indicators, orchard micrometeorological conditions, photosynthetic rate, and chlorophyll fluorescence parameters. The entropy weight method was used to construct EWM-MFM and EWM-VIKOR models for a comprehensive evaluation of treatment effects. The H2T2 treatment (middle canopy, 1.5 h) demonstrated superior canopy cooling and humidification effects for apple trees, promoted stem growth, and exhibited higher photosynthetic rate during both the sprouting and flowering period as well as the fruit setting period. Based on the comprehensive evaluation, H2T2 ranked the highest, whereas H1T4 performed the poorest. Micro spray mist applied at the middle canopy for 1.5 h is recommended as the best-performing tested treatment to improve the canopy microenvironment and enhance apple tree growth and physiological performance. This study provides a practical irrigation solution to mitigate heat-drought stress, thereby advancing precision water management in water-scarce agricultural regions.